Electron microscopic study of operatively removed myocardium from patients with congenital heart diseases associated with muscular obstruction to right ventricular outflow showed that degenerative changes in cardiac muscle cells were much more prevalent and severe in a group of 8 patients aged 30 to 53 years than in a group of 11 patients aged 1 to 5 years. BIBLIOGRAPHIC REFERENCES: Jones, M. and Ferrans, V.J.: Myocardial degeneration in congenital heart disease. Comparison of morphologic findings in young and old patients with congenital heart disease associated with muscular obstruction to right ventricular outflow. Am J Cardiol 39: 1051-1063, 1977.